1. Field of the Invention
The present invention relates to a process cartridge and an image forming apparatus, and more particularly, to a configuration of a developing unit used to supply a developer to a latent image carrier.
2. Description of the Related Art
In an image forming apparatus using an electrophotographic process, image formation is performed by performing a charging process, an exposure process, a developing process, and a transfer process on a photosensitive element used as a latent image carrier.
A developing device including a developing sleeve which is opposed to the photosensitive element is used to supply a developer to the photosensitive element.
A two-component developer which is a mixture of toner and a carrier or a single-component developer which contains no carrier is used in the developing device; even when either one of the developers is used, the developer is carried on the surface of the developing sleeve in the developing device.
The developer carried on the developing sleeve as a developer carrier is maintained at a predetermined layer thickness on the surface of the developing sleeve, and comes in contact with the surface of the photosensitive element.
In the supply of the developer from the developing sleeve to the photosensitive element, there is known a configuration that the developing sleeve is placed to be opposed to the photosensitive element leaving a slight space between them, and the developer is sequentially supplied to the photosensitive element in accordance with the rotation of the developing sleeve, and at the same time, the toner contained in the developer is electrostatically transferred to an electrostatic latent image on the photosensitive element by the application of a developing bias (for example, Japanese Patent Application Laid-open No. H10-282752).
On the other hand, a gear mounted on one end of a rotating shaft in an axial direction is used to drive the developing sleeve in most cases.
In the case where a gear used to drive the developing sleeve is mounted on one end of the rotating shaft in the axial direction, when a driving force acts, the acting force in a radial direction with respect to the rotating shaft differs between both ends of the rotating shaft in the axial direction, i.e., an end which is subject to the driving force and the other end which is not subject to the driving force. Therefore, in the case of a developing sleeve integrated with a rotating shaft mounting thereon a gear as described above, a gap between the developing sleeve and the opposed photosensitive element may vary along the axial direction. This means it becomes in a state where an axis line of the rotating shaft is distorted in the axial direction, and the position of the axis line of the developing sleeve with respect to the photosensitive element is misaligned, and as a result, the gap between the developing sleeve and the photosensitive element varies with location in the axial direction.
Consequently, to resolve such a problem, there has been proposed a configuration that the developing sleeve is pressed toward the shaft center of the photosensitive element thereby preventing a variation in the gap between the developing sleeve and the photosensitive element (for example, Japanese Patent Application Laid-open No. H10-282752).
In addition, as another configuration for preventing a variation in the gap, there has been proposed a configuration that a bearing for supporting the rotating shaft of the photosensitive element is made to have the same outer diameter as the photosensitive element, and a bearing for supporting the rotating shaft of the developing sleeve is made to have a larger outer diameter than that of the developing sleeve and is pressed against the outer circumferential surface of the bearing of the photosensitive element by application of bias by an elastic body, such as a spring, thereby making a gap between the developing sleeve and the photosensitive element equal to a difference between the outer diameter of the bearing of the developing sleeve and the outer diameter of the bearing of the photosensitive element (for example, Japanese Patent No. 2878660).
Furthermore, as a configuration for equalizing the above-mentioned pressing/biasing force of the developing sleeve applied to the photosensitive element in any location in the axial direction, there has been proposed a configuration that the pressing/biasing force is adjusted so that a pull-out force of a film placed in the position at which the photosensitive element and the developing sleeve are opposed is set within a predetermined range (for example, Japanese Patent Application Laid-open No. 2006-48018).
By the way, in recent years, for the purpose of parts recycling, devices built into an image forming apparatus are unitized, thereby improving the attachment and removal operability.
Also in the developing device described above, the attachment and removal operability is required for enabling reuse of the developing sleeve thereby achieving the price reduction; however, in conventional configurations, as for a rotating shaft of a developing sleeve, a configuration that the rotating shaft is inserted into a bearing attached to a unit thereby being supported by the bearing is frequently used, and the unit including the developing sleeve cannot be removed unless the unit is taken apart.